A log parser is a set of regular expressions that are used to parse each line of a particular type of log file (i.e., a computer file that includes a computer data log). The log file may include, for example, a record of system activity events (e.g., login, login failed, logout, and password changed). In currently used techniques for generating log parsers, a user manually writes regular expressions for a log parser using a known interface. The known interface applies each manually written regular expression to a log file and presents information that allows the user to determine whether or not the regular expression is effective.